The ability to perform prospective memory tasks (remembering to perform an action in the future) is essential for maintaining an independent lifestyle. For instance, a person who can not remember to take medication or to turn off the stove will require daily assistance. Understanding how the processes underlying prospective memory performance might differ in younger and older adults is essential for preventing decline and for creating useful means of assistance to those individuals who are having difficulty with this everyday memory task. The proposed research uses mathematical modeling techniques test hypotheses, derived from a new theory of prospective memory, about how age differences in attention and memory interact to produce age differences in prospective memory performance. A mathematical model will be validated and used determine the cognitive processes underlying age differences in prospective memory. Four experiments will evaluate age differences in prospective memory accuracy and age differences in the impact of prospective memory tasks on on-going activities. In addition, the role of resource limitations in older adults? performance on prospective and retrospective tasks will be assessed using a measure of working memory capacity.